Conventional capacitive micromachined ultrasonic transducer (CMUT) device structure provide that the thickness of the membrane is made uniform over the gap or cavity formed between the transducer membrane and the transducer substrate. The thickness and the lateral dimensions of the membrane (or diameter or radius for a circular membrane) as well as the membrane material properties determine the stiffness and the mass of the membrane and therefore determine important device parameters such as capacitance, collapse voltage, and operation frequency. Both the stiffness and the mass of the membrane typically increase as the lateral dimensions and thickness increase. With a uniform membrane thickness, it has heretofore not been possible to control these mass and stiffness parameters separately or independently or even substantially separately or independently or to achieve an optimum transducer performance.
Therefore there remains a need for an ultrasonic transducer device, such as a capacitive micromachined ultrasonic transducer (CMUT) device for which transducer membrane mass and stiffness parameters may be substantially separately or independently controlled so that device parameters such as capacitance, collapse voltage, and operational frequency may be defined to achieve an optimum transducer performance.